1. Technical Field of the Invention
The present invention relates to a printed board having a shield portion, and in particular, to a current/voltage detection printed board that is used to detect an alternating current (AC) voltage generated at a power transmission conductor used as an alternating current power transmission path and an alternating current flowing in the power transmission conductor, and to a current/voltage detector using the current/voltage detection printed board.
2. Description of the Related Art
Like an impedance matching device or a high-frequency power supply device, there is known a device that detects AC power current and voltage and performs a control using the detected current and voltage. As an example, an impedance matching device will now be described.
FIG. 35 is a block diagram of an example of a high-frequency power supply system that uses an impedance matching device.
The high-frequency power supply system is a system that performs a processing, such as plasma etching or plasma CVD, on a workpiece, such as a semiconductor wafer or a liquid crystal substrate. The high-frequency power supply system includes a high-frequency power supply device 61, a transmission line 62, an impedance matching device 63, a load connection portion 64, and a load 65 (plasma processing device 65).
The high-frequency power supply device 61 is a device that outputs high-frequency power to the plasma processing device 65 as a load. Moreover, high-frequency power output from the high-frequency power supply device 61 is supplied to the plasma processing device 65 through the transmission line 62 having a coaxial cable, the impedance matching device 63, and the load connection portion 64 having a shielded copper plate. In general, the high-frequency power supply device 61 outputs high-frequency power having a frequency of a radio frequency band (for example, a frequency of hundreds kHz or more, and just about less than 1 GHz although not strictly-set the upper limit).
The plasma processing device 65 is a device that performs a processing (etching or CVD) on a wafer or a liquid crystal substrate.
The impedance matching device 63 includes a matching circuit that has a variable impedance element (for example, a variable capacitor, a variable inductor, or the like) (not shown) therein. The impedance matching device 63 has a control function of changing impedance of the variable impedance element in the matching circuit to accomplish impedance matching between the high-frequency power supply device 61 and the load 65.
In order to perform the above-described control, a current detector and a voltage detector are provided between an input terminal 63a of the impedance matching device 63 and the matching circuit. The current detector and the voltage detector detect high-frequency current and high-frequency voltage output from the high-frequency power supply device 61. Information of forward wave power or reflected wave power is obtained using the current and voltage detected by the detectors. Then, impedance of the variable impedance element is controlled using the obtained information to accomplish impedance matching.
FIG. 36 is a schematic circuit diagram of a current detector 80 and a voltage detector 90 provided between the input terminal and a matching circuit 67 of the impedance matching device 63. As shown in FIG. 36, a power transmission conductor 66 (for example, rod-shaped copper) serving as a power transmission path is provided between the input terminal 63a and the matching circuit 67. Then, the current detector 80 and the voltage detector 90 are provided on the power transmission conductor 66.
The current detector 80 has a current transformer 81, output wires 82 and 83 of the current transformer 81, a current conversion circuit 84, and an output wire 85 of the current conversion circuit 84. In the current detector 80, a current according to an AC current that flows in the power transmission conductor 66 flows in the current transformer 81. This current is input to the current conversion circuit 84 through the output wires 82 and 83 and is converted into a predetermined voltage level. Then, the converted voltage is output from the output wire 85 of the current conversion circuit 84.
The voltage detector 90 has a capacitor 91, an output wire 92 of the capacitor 91, a voltage conversion circuit 93, and an output wire 94 of the voltage conversion circuit 93. In the voltage detector 90, a voltage according to an AC voltage generated in the power transmission conductor 66 is generated in the capacitor 91. This voltage is input to the voltage conversion circuit 93 through the output wire 92 and is converted into a predetermined voltage level. Then, the converted voltage is output from the output wire 94 of the voltage conversion circuit 93.
Subsequently, as described above, the information of forward wave power or reflected wave power is obtained using the current and voltage detected by the current detector 80 and the voltage detector 90. The current detector 80 and the voltage detector 90 have a structure shown in FIGS. 28 and 29.
FIG. 37 is a schematic exterior view of the current detector 80 and the voltage detector 90.
FIGS. 38A to 38C are explanatory views illustrating the configuration of the current detector 80 and the voltage detector 90 shown in FIG. 37. Specifically, FIG. 38A is a diagram showing the interior of a casing (indicated by a dotted line) of FIG. 27 in perspective view. FIG. 38B is a diagram showing the vicinity of the current transformer 81 as viewed from the transverse side of FIG. 38A. FIG. 38C is a diagram showing the vicinity of the capacitor 91 as viewed from the transverse side of FIG. 38A.
In FIGS. 37 and 38A to 38C, the power transmission conductor 66 and an insulator 69 covering the power transmission conductor 66, not included in the current detector 80 and the voltage detector 90, are shown for explanation. Further, in FIGS. 37 and 38A to 38C, for convenience, the same parts as those in FIG. 36 are represented by the same reference numerals.
Hereinafter, the current detector 80 and the voltage detector 90 will be described with reference to FIGS. 37 and 38A to 38C.
In FIGS. 37 and 38A to 38C, the power transmission conductor 66 is, for example, a cylindrical copper rod. The periphery of the power transmission conductor 66 is covered with a hollow insulator 69. Then, the power transmission conductor 66 and the insulator 69 pass through a casing 71. Further, the current transformer 81 constituting the current detector 80 and the capacitor 91 constituting the voltage detector 90 are accommodated in the casing 71.
In the current transformer 81, a coated copper wire or the like is wound around a ring-shaped magnetic core (for example, a toroidal core made of ferrite) to form a coiled wire. Then, the current transformer 81 is disposed such that the power transmission conductor 66 passes through the magnetic core. Accordingly, a current according to a current flowing in the power transmission conductor 66 flows in the coiled wire of the current transformer 81.
The current flowing in the current transformer 81 is input to the current conversion circuit 84 through the output wires 82 and 83 that are connected to both ends of the coiled wire. Then, the current conversion circuit 84 converts the input current into a predetermined voltage level and outputs the converted voltage.
The capacitor 91 is formed by providing a ring-shaped conductor 91b (for example, a copper ring) in the vicinity of the insulator 69. The ring-shaped conductor 91b and a portion 91a facing the power transmission conductor 66 function as electrodes of the capacitor. Accordingly, a voltage according to the voltage generated in the power transmission conductor 66 is generated in the capacitor 91. The voltage generated in the capacitor 91 is input to the voltage conversion circuit 93 through the output wire 92 connected to the ring-shaped conductor 91b. Then, the voltage conversion circuit 93 converts the input voltage into a predetermined voltage level and outputs the converted voltage.
Moreover, in FIGS. 37 and 38A to 38C, the output wire 85 of the current conversion circuit 84 and the output wire 94 of the voltage conversion circuit 93 are not shown. Further, in order to protect the current conversion circuit 84 and the voltage conversion circuit 93 from an influence of an electromagnetic wave, a common conductor cover 72 is provided to cover the current conversion circuit 84 and the voltage conversion circuit 93. FIG. 37 shows a state where the cover 72 is removed, in order to show the current conversion circuit 84 and the voltage conversion circuit 93. Further, in FIGS. 38A to 38C, the cover 72 is not shown.
As described with reference to FIGS. 37 and 38A to 38C, the current detector 80 and the voltage detector 90 have the casing that covers the current transformer 81, the capacitor 91, and the like, in addition to the parts of the circuit diagram in FIG. 38. The casing is common to the current detector 80 and the voltage detector 90 according to the related art.
The current detector 80 and the voltage detector 90 described above can be used to other devices, such as the high-frequency power supply device 61 or the like. For example, in case of the high-frequency power supply device, the current detector and the voltage detector are provided at an output terminal of the high-frequency power supply device 61. In this case, the current detector and the voltage detector are used to detect current and voltage required for controlling output forward wave power to have a set value.
The current detector and the voltage detector may detect current and voltage at the output terminal 63b of the impedance matching device or the input terminal of the load 65 and may be used to control or analyze the detected current or voltage.
FIG. 39 is a circuit diagram showing a case where the current detector 80 and the voltage detector 90 are provided between the matching circuit and the output terminal in the impedance matching device.
As shown in FIG. 39, the current detector 80 and the voltage detector 90 are provided on the power transmission conductor 68 between the matching circuit 67 and the output terminal 63b in the impedance matching device 63. In this case, the current detector 80 and the voltage detector 90 detect current and voltage at the output terminal 63b of the impedance matching device 63.
In FIG. 39, the same parts as those of the circuit diagram in FIG. 36 are represented by the same reference numerals. Meanwhile, there is a difference in current and voltage at the input terminal 63a and the output terminal 63b of the impedance matching device 63. Accordingly, the current detector 80 and the voltage detector 90 have a structural difference in view of current resistance and voltage resistance. In FIG. 39, the same reference numerals are used regardless of the structural difference. For example, the output terminal 63b of the impedance matching device 63 has higher current and voltage than the input terminal 63a thereof. For this reason, when the current detector 80 and the voltage detector 90 are provided at the output terminal 63b of the impedance matching device 63, it is necessary to extend an insulation length, compared with a case where the current detector 80 and the voltage detector 90 are provided at the input terminal 63a of the impedance matching device 63. In order to extend the insulation length, a conductor having a large diameter is used as the power transmission conductor 68 or the insulator 69 covering the periphery of the power transmission conductor 68 has a large thickness. In FIG. 39, however, for convenience, the structural difference is not considered.
As shown in FIG. 39, when the current detector and the voltage detector are used in the impedance matching device 63, it is necessary to additionally provide a detector for detecting information of current and voltage for impedance matching on the input side of the impedance matching device 63.
Besides, the above examples are disclosed by, for example, JP-A-2003-302431 and JP-A-2004-85446.
Since the current transformer 81 constituting the current detector 80 is formed by winding the wire around the magnetic core, a variation in wiring interval or wiring strength may easily occur. For this reason, when a plurality of current detectors 80 are formed, a variation in detection value of the individual current detectors 80 may easily occur.
Further, a variation in shape of the output wires 82 and 83 of the current transformer 81 may easily occur, which may cause a variation in current detection value.
The inner diameter of the ring-shaped conductor 91b constituting the voltage detector 90 is substantially consistent with the outer diameter of the insulator 69 covering the periphery of the power transmission conductor 66. The ring-shaped conductor 91b is fitted into the insulator 69. That is, the ring-shaped conductor 91b is positioned by the insulator 69. However, the insulator 69 may be thinned due to a secular change or the like. In this case, the position of the ring-shaped conductor 91b may be unstable, and a gap may occur between the power transmission conductor 66 and the insulator 69. In this state, if an external force acts on the power transmission conductor 66, the positional relationship between the power transmission conductor 66 and the ring-shaped conductor 91b changes. Then, a voltage detection value changes from an initial state (upon adjustment of the detector). Besides, since the position of the ring-shaped conductor 91b is unstable, when a plurality of voltage detectors 90 are formed, a variation in detection value of the individual voltage detectors 90 may easily occur.
Further, a variation in shape of the output wire 92 of the ring-shaped conductor 91b may easily occur, which may cause a variation in voltage detection value.
That is, in case of the current detector 80 or the voltage detector 90, when a plurality of detectors are formed, a variation in detection value of the individual detectors may easily occur.
Further, since the wire is wound around the core in the current transformer 81 constituting the current detector 80, there is a self-resonant frequency by self inductance and line capacitance. However, since relative magnetic permeability of a magnetic material used for the core is large, the self-resonant frequency becomes low. For this reason, an upper limit of a detectable frequency band becomes low. That is, the detectable frequency band is limited.
The current detection point and the voltage detection point are preferably the same, but as shown in FIGS. 38A to 38C, the current detection point and the voltage detection point may be away from each other in the axial direction of the power transmission conductor 66.